UPLOCK
1DOOR CLOSEDUP DOWN
CLOSE
2
DURING DOOR MOVEMENT LOCK NOSE LANDING GEAR FORWARD NOSE LANDING GEARNOSE LANDING GEAR LOCK3
DOOR OPEN
DOOR ACTUATOR RETRACT ACTUATOR ACTUATOR
Nose Landing Gear Extension and Retraction Operation Schematic
Figure 6 (Sheet 1)

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MAINTENANCE MANUAL

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HYDRAULIC POWERLEFT HYDRAULIC
TRANSFER UNIT SYSTEM POWER

DOWN UP OFF
RESTRICTOR
RELIEF VALVE

LANDING GEARSELECTOR VALVE
TO MAIN LANDING
GEAR SYSTEMS

DOWN DURING GEAR MOVEMENT UP
1 2 2 3
LOCK UNLOADVALVE MODULE
NOSE LANDING GEAR GEAR-OPERATEDSEQUENCE VALVENOSE LANDING GEAR DOOR-OPERATED SEQUENCE VALVE PRESSURE-
OPERATED
CHECK
VALVE DOORSAFETYUNLOCK FLOW CONTROL VALVE
VALVE
NOSE LANDING GEAR DOOR
RELEASE INTERLOCK
ACTUATOR
RESTRICTOR
UP
CHECK VALVE
LOCK
1DOOR CLOSED
UP
DOWN
CLOSE
2DURING DOOR MOVEMENT
LOCK
NOSE LANDING GEAR FORWARD NOSE LANDING GEAR
NOSE LANDING GEAR LOCK
3 DOOR OPEN
DOOR ACTUATOR RETRACT ACTUATOR
ACTUATOR
Nose Landing Gear Extension and Retraction Operation Schematic
Figure 6 (Sheet 2)

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 (f)  
When the gear is fully retracted, the lock actuator retracts, again. This pulls the lock links back overcenter to lock the landing gear up.

 (g)  
The position of the gear sequence valve bypass valve is now changed to pressurize the retract actuator as the doors close.

 (h)  
The gear-operated sequence valve again sends hydraulic fluid through the door safety valve. This pressurizes the door actuator to retract to close the doors.

 (2)  
Landing Gear Extension

 (a)  
Hydraulic fluid flows through the gear-operated sequence valve and the flow control valve. This pressurizes the door actuator to extend and the doors start to open.

 (b)  
As the doors open, hydraulic fluid flows through the door-operated sequence valve to pressurize the lock actuator to extend. The lock actuator pushes the lock links from the overcenter position and releases the landing gear from the up and locked position.

 (c)  
As the doors open, the landing gear extends because of its weight. During landing gear extension, movement of the lock link causes the lock actuator to retract. Hydraulic pressure is still applied to extend the actuator, but this does not prevent lock actuator retractioin.

 (d)  
When the landing gear is fully extended, the lock actuator extends again. This pushes the lock links back overcenter to lock the landing gear down.

 (e)  
The gear-operated sequence valve again sends hydraulic fluid through the door safety valve. This pressurizes the door actuator to retract to close the doors. Fluid from the door actuator that flows to return goes through the flow control valve, where the flow is limited. This decreases the speed at which the door closes.

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757 MAINTENANCE MANUAL
 NOSE GEAR EXTENSION AND RETRACTION - ADJUSTMENT/TEST
____________________________________________________
 TASK 32-34-00-715-017
 1.  Operational Test - Nose Landing Gear Extension and Retraction_____________________________________________________________
 A. General
 (1)  
This test does a check of the extension and retraction system for the nose landing gear to ensure satisfactory performance. The test does not contain the data for a full system test or adjustment of the extension and retraction system.

 B.
Equipment

 (1)  
Stop Watch

 C.
References

 (1)  
07-11-02/201, Jacking Airplane Nose

 (2)  
　
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航空翻譯 www.aviation.cn
本文鏈接地址：757 AMM 飛機維護手冊 起落架 CHAPTER 32 - LANDING GEAR 2(76)